EP0541775B1

EP0541775B1 - Acoustic web edge sensor

Info

Publication number: EP0541775B1
Application number: EP92912634A
Authority: EP
Inventors: Michael Alan Marcus
Original assignee: Eastman Kodak Co
Current assignee: Eastman Kodak Co
Priority date: 1991-05-29
Filing date: 1992-05-27
Publication date: 1996-07-10
Anticipated expiration: 2012-05-27
Also published as: DE69212115T2; JPH06500638A; EP0541775A1; DE69212115D1; WO1992021935A1; US5161126A

Abstract

A method and apparatus for sensing the edge of a web (14) which moves along a surface (16) of a body (22) wherein an acoustic pipe is provided in the body with an opening (32) located so that the edge (12) of the web covers a portion of the opening as a function of the position of the web, an air column (20) in the pipe is caused to resonate so that the resultant acoustic signal has a frequency spectrum which is a function of the portion of the opening which is covered by the web, and the resultant acoustic signal is utilized to provide information relating to the location of the edge of the web. The opening can comprise a series of spaced apertures (32), some of which are covered by the web, or a continuous slot (100) which is partially covered by the web. The resultant acoustic signal can be analyzed by scanning a range of signal frequencies to determine the location of the edge of the web. A web width sensor comprises a pair of adjacent web edge sensors (101, 102), one for sensing the location of each web edge, for determining web width.

Description

The present invention is concerned with a sensor for sensing at least one edge of a workpiece comprising the features of the pre-characterizing clause of claim 1. Such a sensor is known from US-A-4,850,232.
The invention is also concerned with a corresponding method of sensing at least one edge of a workpiece.
One area of use of the present invention is in material handling where it is desired to sense the edge of a web of material passing along a surface, although the principles of the invention can be variously applied. An example is sensing or measuring the edge of a paper or film web as it is passing a roller surface. Prior art arrangements exist which utilize transmitted energy such as light or ultrasonic energy to measure one or more dimensions of a workpiece such as sheet material. Such arrangements often are complex and typically provide transmitting and receiving or detecting components on opposite sides of the sheet of material which intercepts the energy beams between the components.
It would, therefore, be highly desirable to provide a new and improved edge sensing method and apparatus which is relatively simple in structure and operation and which provides relatively high resolution. In particular, the apparatus and method according to the present invention shall have relatively low energy requirements. The method and apparatus also shall be readily adaptable to a material handling apparatus.
These technical problems are solved by a sensor according to claim 1. Preferred embodiments of said sensor are disclosed in dependent claims 2 to 11.
A method solving the above technical problem is disclosed in claim 12. Dependent claims 13 to 15 describe preferred embodiments of said method.

Brief Description Of The Drawings

Fig. 1a is a diagrammatic view of an acoustic flute web edge sensor according to the present invention;
Fig. 1b is a diagrammatic view of an alternative form of the acoustic flute web edge sensor shown in Fig. 1a;
Fig. 2 is a diagrammatic view illustrating the transmitting/receiving means in the sensor of Fig. 1:
Fig. 3 is a schematic block diagram further illustrating the sensor of Fig. 1;
Figs. 4 and 5 are graphs including waveforms illustrating operation of the sensor of Fig. 1;
Fig. 6 is a diagrammatic view illustrating an alternative form of transmitting/receiving means in the sensor of the present invention;
Fig. 7 is a schematic block diagram illustrating an alternative form of the sensor of the present invention;
Fig. 8 is a diagrammatic view illustrating an alternative form of opening in the sensor of the present invention; and
Fig. 9 is a diagrammatic view of an acoustic flute web width sensor according to the present invention.

Modes of Carrying Out The Invention

The edge sensor according to the present invention employs an acoustic flute or resonator in the form of a pipe or other surface containing a plurality of holes or a continuous slot positioned so that the edge of a web covers a portion of the slot or a number of holes as a function of its position. The air column in the pipe is caused to vibrate and the resultant acoustic signal has a resonant frequency spectrum which varies as the number of holes or portion of the slot covered by the web is varied. The resultant acoustic signal is analyzed to provide information relating to the location of the edge of the web. In particular, a signal detection means scans a range of signal frequencies to determine the number of holes uncovered on the portion of the slot uncovered.
Referring now to Fig. 1a, there is shown a sensor 10 of the present invention to measure the edge 12 of a paper or film web 14 as it is passing the surface 16 of a roller 18. The edge position sensor 10 consists of an acoustic flute built into the surface of the roller.
Fig. 1 shows a sectional view of roller 18 with the acoustic flute structure embedded in the roller. In particular, there is provided an acoustic pipe comprising a fluid conducting region 20 of determinate length in the body 22 of roller 18. The pipe is closed at each end, i.e. by surface 24 at one end as shown in Fig. la and by the transmitting/receiving means 30 at the other end which will be described. The pipe has an opening between the ends for placing region 20 in fluid communication with surface 16. In this embodiment, the opening is provided by a series of spaced apertures 32 provided in the body 22 each extending radially outwardly from region 20 through surface 16. Preferably apertures 32 are of constant and equal diameter, equally spaced and extend along a substantially linear path. The holes 32 are of relatively small cross-sectional size or area. Advantageously, passage 20 and apertures 32 simply can be drilled in roller body 22 so that sensor 10 can be readily incorporated in existing rollers or the like.
During normal operation of sensor 10, it is assumed that the web 14 comes in contact with the roller 18, and that some of the holes 32, in the acoustic flute structure are normally covered. If the web 14 moves laterally a different number of holes 32 in the acoustic flute will be open, which affects the resonance frequency spectrum of the structure. As an example consider the case where 1/32" lateral resolution is required. To meet this requirement the individual hole diameters must be less than 1/64" and be spaced by 1/32".
The principle of operation is as follows. The fundamental resonance frequency of the structure increases as more holes 32 are covered, i.e. as web edge 12 moves to the left in Fig. 1a. Since the volume of the holes 32 is extremely small, very little air pressure, i.e. energy, is required to operate the sensor and drive the circuit. The far end of the pipe as shown in Fig. 1 is driven by means 30 which can comprise a piezoelectric transmitter/receiver which provides both excitation and reception of the resonance frequency.
While the transmitting receiving pair 30 is located on the left-hand side of the arrangement in Fig. 1a, i.e. laterally outwardly of the web edge 12, it can also be located on the right-hand side of the alternative form of sensor shown in Fig. 1b wherein like components are designated by the same reference numeral provided with a prime designation. In particular, sensor 10' measures edge 12' of web 14' as it passes over surface 16' of roller 18'. An acoustic pipe comprises a fluid conducting region 20' of determinate length in body 22' of roller 18', and the pipe is closed by a surface 34 at one end and by the transmitting/receiving means 30' at the other end. In this embodiment surface 34 is laterally outwardly of web edge 12' and transmitter/receiver 30' is laterally inwardly of web edge 12'. The acoustic pipe opening is provided by a series of spaced apertures 32' in body 22' extending radially outwardly from region 20' through surface 16' which apertures 32' are of relatively small cross-sectional size or area. Preferably apertures 32' are of constant and equal diameter, equally spaced and extend along a substantially linear path.
Sensor 10' operates according to the same principle as sensor 10, i.e. as web 14' moves laterally on roller 18' a different number of holes 32' in the acoustic flute will be open, which affects the resonance frequency spectrum of the structure. However, in sensor 10' the resonance frequency will decrease as more holes 32' are covered by web 14', i.e. as web edge 12' moves to the left as viewed in Fig. 1b.
One form of transmitting/receiving means 30 is shown in Fig. 2. There is provided a single pipe acoustic transducer configuration in which two polyvinylidene fluoride (PVF₂) transducers 36 and 38 are layered adjacent each other at the one end of pipe 20. In particular, transmitting transducer 36 is in the form of a disc held in place by mounting ring 40 and receiving transducer 38 also is in the form of a disc held in place by a mounting ring, The discs are separated by a shield 44 of metal or like conductive material which serves as a ground plane between the two transducers 36,38 for RFI shielding. The transducers are located within a conductive housing 46 which provides additional shielding for receiving transducer 38 to eliminate unwanted noise sources. Electrical leads (not shown in Fig. 2) from transducers 36,38 are connected to a terminal structure 48 insulated from housing 46 for making electrical connection to the transducer driving and detecting circuitry which will be described.
Polyvinylidene fluoride (PVF₂), a polymer which exhibits piezoelectric and pyroelectric properties when appropriately polarized, is preferred as the transmitter T and receiver R material. However, the transmitter T and receiver R can be ceramic piezoelectric transducers as well. In fact, transmitter T can be any acoustic generator means including moving diaphragm loudspeakers or air jets. The receiver R can be any kind of microphone.
Miniature PVF₂ acoustic transducers which are coupled to miniature pipes, such as transducers 36,38 coupled to pipe 20, utilize both the direct and converse piezoelectric effects. A PVF₂ transmitter (electromechanical converter) like disc 36 sends acoustic energy down a pipe like passage 20. Acoustic energy is either transmitted through the pipe orifice i.e. apertures 32, or reflected to a second PVF₂ transducer used as a receiver of acoustic energy (mechano-electric converter) like disc 38. Changing the state of the orifice such as closing the hole or moving an object near it changes the amplitude and/or phase of the electrical signal produced by the receiving transducer. When the electrical drive frequency is adjusted to a mechanical pipe resonance large increases in sensitivity occur. This is due to the fact that if a pipe is tuned for an open resonance closing the port will frustrate the resonance and destroy the standing wave. Similarly, if the pipe is tuned for a closed resonance opening the port will destroy the standing wave, thus decreasing the acoustic energy incident upon the receiver.
For more information on the general operation of acoustic transducer arrangements, reference may be made to United States Patent No. 3,694,800 issued September 26, 1972 entitled "Acoustical Gauge". For more information on the structure and operation of a transmitting and receiving pair like that shown in Fig. 2, reference may be made to United States Patent No. 4,494,841 issued January 22, 1985 entitled "Acoustic Transducer For Acoustic Position Sensing Apparatus".
Various approaches are available for the drive/detection circuitry associated with transducers 36,38. According to one approach, the acoustic pipe 20 is excited with a linear combination of all of the resonance frequencies, and the relative intensitites of these frequencies are analyzed. In particular, a clock pulse starts a frequency ramp, and the receiver amplitude is measured as a function of time from initiation of the clock pulse. The time interval for the maximum signal is determined which locates which hole 32 the web edge 12 is on. A circuit for implementing this approach is shown in Fig. 3. Transmitting transducer 36 is driven by a function generator 54 under control of a clock 56. The output pulse from clock 56 starts the frequency ramp provided by generator 54, and waveform 58 in Fig. 4 illustrates the frequency ramp output of generator 54. The output of receiver 38 is connected to the input of an amplifier-threshold detector combination 60 which, in turn, is connected to the input of an analog to digital converter 62 which provides digital signal inputs to a microprocessor 64.
The output signal from receiver 38 is illustrated by the waveforms in Fig. 5. In particular, waveform 70 represents the receiver output when three holes 32 are covered by web 14 and waveform 72 represents the receiver output when four holes 32 are covered by web 14. The operation is based on the fact that transmitter 36 and pipe 20 are tuned for closed tube resonance such that as more holes 32 are covered by web 14 the resonance frequency of the structure increases. By way of further illustration, the frequencies for closed pipe resonance are given by the relationship $fn = \frac{2n - 1}{4} \frac{c}{L}$
where n is an integer, c is the speed of sound and L is the length of the acoustic pipe.
The frequency information in the receiver output is digitized and supplied to microprocessor 64 which previously has been provided with information as to the resonant frequency for each hole location so that microprocessor 64 can map the frequency signal from receiver 38 to a particular hole location thereby determining the location of the edge 12 of the web 14.
In the sensor 10 shown in Figs. 1a and 1b, a combined transmitter/receiver 30 is provided at the one end of acoustic pipe 20. Alternatively, separate transmitter and receiver components can be provided at opposite ends of the acoustic pipe as shown in Fig. 6 wherein components identical to those of the sensor of Fig. 1 are indentified by the same reference numeral having a double prime designation. Thus a transmitter 76 is provided at the left-hand end of pipe 20" as shown in Fig. 6 and transmitter 76 can comprise a PVF2 disc within a housing according to the arrangement of Fig. 2. Similarly, a receiver 78 is provided at the right-hand side end of pipe 20" as shown in Fig. 6 and receiver 78 can comprise a PVF2 disc within a housing according to the arrangement of Fig. 2.
As previously described, other transmitter and receiver materials can be employed. The spaced - apart transmitter and receiver components are connected by electrical leads (not shown) to a driver/detector circuit like that of Fig. 3.
According to another approach for the drive/detection circuitry for transducers 36, 38 a white noise burst is sent down acoustic pipe 20 and the return signal is analyized by taking its Fourier transform to determine its resonance frequency spectrum. The Fourier transform looks at the frequency spectrum of the noise burst. As the web edge position is altered, different frequency components will be maximized as a function of the position of the web. A circuit for accomplishing the foregoing is illustrated in Fig. 7 and features a self-tuned oscillator designated 80 which functions to look for the maximum signal at the receiver output and picks out that frequency. The self-tuned oscillator provides increased power output at the resonant frequency. In the circuit of Fig. 7, the combination transmitter/receiver 82 similar to transmitter/receiver 30 of Fig. 1 and a voltage-dropping resistance 84 are connected to self-tuned oscillator 80. The voltage /time signal appearing across resistance 84 is applied to the input of a sample and hold circuit 86 which holds the maximum signal for measurement by a processing circuit 90. From the voltage/time signal, frequency information is obtained and by comparing this to the frequencies of the hole locations, the frequency information in the voltage/time signal can be mapped to the hole locations thereby providing information as to the location of the web edge. In certain acoustic flute designs more than one local maxima in frequency may be needed in order to determine web position.
An alternative to the individual holes 32 shown in Figs. 1a and 1b is to provide a continuous elongated narrow slot 100 in the body of roller 18"' as shown in Fig. 8. Slot 100 is in communication with acoustic pipe 20"' which has a transmitter/receiver 30"' associated therewith as in the previous embodiment. While transmitter/receiver 30"' is shown in the location of Fig. la, it could be located as shown in Fig. 1b. Slot 100 is partially covered by web 14", and the resonance frequency increases as the effective length of slot 100 is decreased in response to movement of web 14"'.
The same driver/detection circuits are used to provide information as to the location of web edge 12", and as in the precious embodiment the useful operating frequency range is 10KHZ to 100KHZ.
Fig. 9 illustrates an acoustic flute web width sensor according to the present invention including first and second web edge sensors 101,102 located adjacent each other along the direction of travel of a web 104 and operatively associated with corresponding ones of the opposite web edges 106,108. Typically the sensor of Fig. 9 is used to sense the width of web 104 as it travels over the surface of the roller designated 110, and in this situation sensors 101,102 are built into roller 110. Alternatively, the two sensors 101,102 can be in a pair of rollers facing each other which are in contact at a nip.
In particular, sensor 101 is an acoustic flute web edge sensor similar to sensor 10' shown in Fig. 1b and is used to sense the location of web edge 106. The transmitting/receiving means 112 of sensor 101 is located so that a major portion of sensor openings 114 are located between web edge 106 and transmitter/receiver 112. As a result, as the number of openings 114 covered by web 104 increases, i.e. as web edge 106 moves to the left in Fig. 9, the resonance frequency decreases. Similarly, sensor 102 is an acoustic flute web edge sensor similar to sensor 10' shown in Fig. 1b and is used to sense the location of web edge 108. The transmitting/receiving means 118 of sensor 102 is located so that a major portion of sensor openings 120 are located between web edge 108 and transmitter/receiver 118. As a result, as the number of openings 120 covered by web 104 increases, i.e. as web edge 108 moves to the right in Fig. 9, the resonance frequency decreases.
The location of the position of both edges 106,108 by the foregoing arrangement effectively determines web width. Each of the sensors 101,102 would be provided with appropriate drive/detection circuitry like that shown and described in connection with Figs. 3 and 7. An example of the web width sensor of Fig. 9 has applicability to a photoprocessor. The two sensor system is used to monitor sheet width. Film of unknown width is fed into the photoprocessor through the measurement rollers at a constant rate. The film is developed in the photoprocessor. The frequency of photoprocessing chemical replenishment is dependent upon the area of film treated. The width of web fed into the photoprocessor would be tracked as a function of time and chemicals added as needed. The web width sensor of Fig. 9 would be incorporated in one of the measurement rollers.
By way of further illustration, multiple sets of flute transducers can be provided in a roller if necessary to enhance the sampling rate, since the flute is active only where the web is perpendicular to the holes. Furthermore, while the sensor of the present invention has been described in connection with a roller, it can be employed in other material handling apparatus and in other structures where it is desired to sense the location of the edge of a stationary or moving web.
It is therefore apparent that the present invention accomplishes its intended objects. There is provided a new and improved edge sensing method and apparatus which employs acoustic energy, which has relatively low energy requirements, and which achieves relatively high resolution. The sensor is relatively simple in structure and operation and is readily adaptable to existing material handling and like apparatus.
While embodiments of the present invention have been described in detail, that is for the purpose of illustration, not limitation.

Claims

A sensor for sensing at least one edge of a workpiece, such as a sheet, comprising means (T/R) for transmitting acoustic energy and means (T/R) for receiving acoustic energy,
characterized by
at least one acoustic pipe (20, 32; 20', 32'; 20"', 100) having an opening (100) or openings (32; 32') located so that the work piece (14; 14'; 14") covers a portion of said opening (100) or more or less of said openings (32; 32') as a function of the position of said edge, wherein said pipe produces an acoustic signal when receiving acoustic energy, and wherein said acoustic signal produced by said pipe is received by said receiving means (T/R; R) and contains information as to the location of said edge relative to said opening (100) or openings (32; 32').
A sensor according to claim 1,
characterized in that
said transmitted acoustic energy causes an air column in said pipe to resonate.
A sensor according to one of the claims 1 or 2,
characterized in that
said means for transmitting acoustic energy and said means for receiving acoustic energy are combined.
A sensor according to one of the preceding claims,
characterized by
means (Fig. 7) for scanning a range of frequencies of said acoustic signal produced by said pipe to determine the location of said edge.
A sensor according to claim 2,
characterized in that
said means for causing said air column to resonate comprises means for sending a white noise burst along said pipe and wherein said utilizing means comprises signal analyzing means for determining the resonant frequencies of the return signal utilizing the Fourier transform thereof.
A sensor according to claim 2,
characterized in that
said means for causing said air column to resonate comprises means for exciting the acoustic pipe with a linear combination of all of the resonant frequencies of said pipe and means for analyzing the relative intensities of said resonant frequencies.
A sensor according to claim 4,
characterized in that
a detection means for detecting the frequencies includes a self-tuned oscillator.
A sensor according to one of the preceding claims,
characterized in that
said opening comprises a series of spaced apertures and said workpiece covers at least some of said apertures.
A sensor according to one of the claims 1 to 7,
characterized in that
said opening comprises a continuous slot and said workpiece covers a portion of said slot (100).
A sensor according to claim 8,
characterized in that
the spacing between individual apertures is equal to the required lateral resolution in the location of the edge of said workpiece and the dimension of each aperture in a lateral direction is one-half the required lateral resolution.
A sensor according to one of the preceding claims,
characterized in that
two acoustic pipes (Fig. 9) are provided for sensing two opposing edges of a workpiece (WEB) so that the width of the workpiece is determined.
A method for sensing the edge of a workpiece,
characterized by the steps:
- causing an air column in a pipe having at least an opening or openings located so that the edge of the workpiece covers a portion of the opening or of the openings as a function of the position of the workpiece to resonate so that the resultant acoustic signal has a resonant frequency spectrum which is a function of the portion of the opening or openings which is covered by the workpiece; and

- utilizing the resultant acoustic signal to provide information relating to the location of said edge of said workpiece.
A method according to claim 12,
characterized in that
said step of utilizing the resultant acoustic signal includes scanning a range of signal frequencies to determine the location of said edge of said workpiece.
A method according to claim 13,
characterized in that
said step of causing said air column to resonate comprises sending a white noise burst along said pipe and wherein said steps of utilizing the resultant signal comprises analyzing the return signal by taking the Fourier transform thereof to determine the resonant frequency spectrum of the signal to determine the location of the edge of said workpiece.
A method according to claim 13,
characterized in that
said step of causing said air column to resonate comprises exciting said acoustic pipe with a linear combination of all of the resonant frequencies and wherein said step of utilizing the resultant signal comprises analyzing the relative intensities of said frequencies to determine the location of the edge of said web.